The melancholy tale of lost love sports only Mars' vocals and his own piano accompaniment.

Amazingly, of the 1,023 songs to previously top the chart, dating to its Aug. 4, 1958, launch, just one also features nothing but vocals and piano: Adele's "Someone Like You," which ruled for five weeks beginning on Sept. 17, 2011. The song showcases Adele singing and Dan Wilson on piano.

With its 2-1 lift this week, "Man" is the first ballad to top the Hot 100 since "Someone." Before Adele's ascension, no ballad had reigned since Rihanna's "Take a Bow" the week of May 24, 2008. "Man" is the first No. 1 ballad by a male since Akon's "Don't Matter," which led the Hot 100 the weeks of April 7 and 14, 2007.

Songs like "Bow" and "Matter," however, include instrumentation beyond piano. Much more uncommon is a hit compelling enough for pop radio to slow its tempo to only a voice and piano without drums, strings or other sonic elements.

Throughout the Hot 100's history, piano ballads have reigned, but until Adele and Mars' songs, none were as stripped down as "Someone" and "Man." All-piano-and-vocal hits have charted, but none previously had reached No. 1. Sarah McLachlan's "Angel," for example, rose to No. 4 in 1999.

A chronological trip back through the Hot 100's archives reveals examples of No. 1 piano ballads, but all include other instrumentation.

Updating a recap first published on Billboard.com when "Someone" reached No. 1, let's time-travel through the chart's past … keying … in on some of the most notable such hits.

2000sThe 2000s (through this year) have brought such piano-intensive No. 1s largely courtesy of Fox's "American Idol" coronation songs, including Carrie Underwood's "Inside Your Heaven" (2005) and Fantasia's "I Believe" (2004). Plus, in 2005, the series' original winner, Kelly Clarkson, reached No. 7 with "Because of You." None of those songs, however, are as bare-bones as "Man" or "Someone."

Following Mars' "Man," could another pure all-piano ballad soon reign?Rihanna's current hit "Stay," featuring Mikky Ekko, features only their vocals and piano by Justin Parker. The song rebounds to No. 4 this week, having risen as high as No. 3 so far.

1990sDuring the decade when the pure-pop boy band dominations of New Kids on the Block and 'N Sync and Backstreet Boys sandwiched the rise of grunge, Elton John performed "Candle in the Wind 1997" (on Sept. 6, 1997) on piano at the funeral of Princess Diana of Wales. When he released a new studio version of his '70s classic as a single (paired with "Something About the Way You Look Tonight"), "Candle" included orchestration by its conclusion. Thus, while it's an unquestionably a piano ballad (and half of a double-sided 14-week No. 1), it's not 100% so.

The '90s brought other leading piano ballads, but all also with varying degrees of strings, guitars or drums, including Carey's "Hero" and Janet Jackson's "Again" (1993); Carey's "I'll Be There" and Vanessa Williams' "Save the Best for Last" (1992); and, Stevie B's "Because I Love You (The Postman Song)" (1990).

(Also in 1992-93: while not the prototypical piano ballad, considering its signature saxophone and drum flourishes, Whitney Houston's "I Will Always Love You," which logged 14 weeks at No. 1, is notable in that its vocal impact is similar to that of "Man" and "Someone," as Houston's hit opens with a 44-second a capella intro.)

And, one from the original Piano Man: At the beginning of the '90s, the fifth and final single from Billy Joel's Billboard 200 No. 1 album "Storm Front" was an all-piano ballad pop hit. "And So It Goes," however, just dented the Hot 100's top 40, reaching No. 37 in December 1990.

Two mixes exist of Bette Midler's "The Rose": the single edit with orchestration and the soundtrack version that sports piano and vocals-only. The song just missed topping the Hot 100, however, reaching No. 3 in 1980.

(Honorable mention: Bobby McFerrin scored the Hot 100's first a capella No. 1 with "Don't Worry, Be Happy," which led for two weeks in 1988.)

Even Barry Manilow's three piano-centric No. 1s – "Looks Like We Made It," "I Write the Songs" and Mandy" – are string-laden, as are the Beatles' last two No. 1s, "The Long and Winding Road" and "Let It Be," along with John Lennon's "Imagine," a No. 3 hit in 1971.

In February 1970, Simon & Garfunkel began a six-week reign with "Bridge Over Troubled Water." Art Garfunkel's vocal and Larry Knechtel's piano arrangement carry most of the song. But, strings and drums arrive near its closing.

1960s/'50sNot too many ballads of any kind ruled the Hot 100 during the decade, as the Beatles helped craft an era of, largely, jangly pop/rock toppers. Pre-British Invasion, tempo also was an almost exclusive Hot 100 No. 1 ingredient, although with fewer guitars and more orchestral arrangements.

Piano-dominated songs hit big in the early '60s and late '50s, but the instrument in those years tended to serve as an uptempo component of early rock and roll (i.e., Chuck Berry, Dave "Baby" Cortez and Fats Domino) or the focus of fast-paced instrumentals, such as Floyd Cramer's "Last Date" (a No. 2 hit in 1960).

In all, just two piano-and-vocal-only No. 1 ballads among 1,024 Hot 100 leaders: Mars' " Man" and Adele's "Someone." Notably, both have reached the summit in the past year-and-a-half.

With more tools available when it comes to music production, perhaps ballads stand out more now, helping to make the most compelling of such songs rarer, and, thus, more appreciated than ever before.